Characterization of Photosynthetic Rhythms in Marine Dinoflagellates: II. Photosynthesis-Irradiance Curves and in Vivo Chlorophyll a Fluorescence.

Using data from light-dark cultures of Gonyaulax polyedra entrained to a 24-hour cycle, whole cell absorption curves and photosynthesis-irradiance curves were constructed for various circadian times. While whole cell absorbance and half-saturation constants of photosynthesis showed no statistical difference that could be directly related to the photosynthetic rhythm, the initial slope of the photosynthesis-irradiance curve was a time-dependent parameter which altered in direct proportion to the change in photosynthetic capacity. The results indicated a temporal change in the relative quantum yield of photosynthesis, and the circadian rhythmicity of light-limited photosynthesis was established under constant conditions. Circadian rhythmicity was detected in room temperature chlorophyll fluorescence yield. Low temperature fluorescence kinetics also showed fluctuations. The results suggest that regulation of photosynthesis by the biological clock of Gonyaulax may be mediated through the membrane-bound light reactions and a partial explanation of the underlying mechanism is proposed.